Photonic package and method forming same

ABSTRACT

A method includes bonding an electronic die to a photonic die. The photonic die includes an opening. The method further includes attaching an adapter onto the photonic die, with a portion of the adapter being at a same level as a portion of the electronic die, forming a through-hole penetrating through the adapter, with the through-hole being aligned to the opening, and attaching an optical device to the adapter. The optical device is configured to emit a light into the photonic die or receive a light from the photonic die.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.15/725,911, entitled “Photonic Package and Method Forming Same,” filedon Oct. 5, 2017, which application claims the benefit of the followingprovisionally filed U.S. Patent application: Application Ser. No.62/527,185, filed Jun. 30, 2017, and entitled “Photonic package andmethod forming same,” which application is hereby incorporated herein byreference.

BACKGROUND

Electrical signaling and processing have been the mainstream techniquesfor signal transmission and processing. Optical signaling and processinghave been used in increasingly more applications in recent years,particularly due to the use of optical fiber-related applications forsignal transmission.

The optical signaling and processing are almost always combined withelectrical signaling and processing to provide full-fledgedapplications. For example, the optical fibers may be used for long-rangesignal transmission, while electrical signals may be used forshort-range signal transmission as well as processing and controlling.Accordingly, the devices integrating optical components and electricalcomponents are formed for the conversion between optical signals andelectrical signals, as well as the processing of optical signals andelectrical signals. Packages thus may include both optical (photonic)dies including optical devices and electronic dies including electronicdevices.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A through 1G illustrate the cross-sectional views of intermediatestages in the formation of a chip-on-wafer package including bothoptical devices and electrical devices in accordance with someembodiments.

FIGS. 2 and 3 illustrate the packages including both optical devices andelectrical devices in accordance with some embodiments.

FIGS. 4A through 4D illustrate the cross-sectional views of intermediatestages in the formation of a chip-on-chip package including both opticaldevices and electrical devices in accordance with some embodiments.

FIGS. 5A through 5D illustrate the cross-sectional views of intermediatestages in the formation of a chip-on-wafer package including bothoptical devices and electrical devices in accordance with someembodiments.

FIGS. 6A through 6C illustrate the cross-sectional views of intermediatestages in the formation of adapters in accordance with some embodiments.

FIG. 7A illustrates the cross-sectional view in the formation of anadapter in accordance with some embodiments.

FIGS. 7B through 7G illustrate the top views and cross-sectional viewsof intermediate stages in the formation of an adapter in accordance withsome embodiments.

FIGS. 8 and 9 illustrate top views of some adapters and thecorresponding Grating Coupler (GC) holes in accordance with someembodiments.

FIG. 10 illustrates a process flow for forming a chip-on-wafer packagein accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “underlying,” “below,”“lower,” “overlying,” “upper” and the like, may be used herein for easeof description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. Thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. The apparatus may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

A three-dimensional (3D) package including both optical devices andelectrical devices and the method of forming the same are provided inaccordance with various exemplary embodiments. The intermediate stagesof forming the packages are illustrated in accordance with someembodiments. Some variations of some embodiments are discussed.Throughout the various views and illustrative embodiments, likereference numbers are used to designate like elements.

FIGS. 1A through 1G illustrate the cross-sectional views of intermediatestages in the formation of a package in accordance with some embodimentsof the present disclosure. The steps shown in FIGS. 1A through 1G arealso reflected schematically in the process flow 200 shown in FIG. 10.

FIG. 1A illustrates a cross sectional view of photonic die 10, which ismounted on carrier 2 through adhesive 4. The respective step isillustrated as step 202 in the process flow shown in FIG. 10. Inaccordance with some embodiments of the present disclosure, photonic die10 is a part of wafer 6, which includes a plurality of identicalphotonic dies 10 arranged as an array, although one photonic die 10 isillustrated in detail. Photonic die 10 has the function of receivingoptical signals, transmitting the optical signals inside photonic die10, transmitting the optical signals out of photonic die 10, andcommunicating electronically with electronic die 54. Accordingly,photonic die 10 is also responsible for the Input-Output (IO) of theoptical signals.

Photonic die 10 includes substrate 12. Substrate 12 may be asemiconductor substrate, which may be a silicon substrate, a silicongermanium substrate, or a substrate formed of other semiconductormaterials. In accordance with alternative embodiments of the presentdisclosure, substrate 12 is a dielectric substrate formed of, forexample, silicon oxide. In accordance with some embodiments of thepresent disclosure, photonic die 10 is used as an interposer, andincludes Through-Vias (TVs, also referred to as through-substrate viasor through-silicon vias) 14 penetrating through substrate 12. TVs 14 areformed of a conductive material, which may also be a metallic materialsuch as tungsten, copper, titanium, or the like. Isolation layers 16encircle TVs 14, and electrically isolation TVs 14 from substrate 12.

The process shown in FIGS. 1A through 1G are referred to as asolder-first process, in which the backside structure (including solderregions 26) of photonic die 10 is formed first, as shown in FIG. 1A. Inthe structure shown in FIG. 1A, dielectric layer 18 is underlyingsubstrate 12, and may be formed of silicon oxide, silicon nitride,silicon carbide, or other dielectric materials. TVs 14 may penetratethrough dielectric layer 18. Redistribution Lines (RDLs) 22 are formedunderlying and connected to TVs 14, and are used for reroutingelectrical signals, power, electrical ground, or the like.Redistribution lines 22 are formed in dielectric layers 20. Under-BumpMetallurgies (UBMs) 24 are formed as being underlying and electricallyconnecting to RDLs 22, and solder regions 26 are formed on UBMs 24.

In accordance with some embodiments of the present disclosure,integrated circuit devices 28 may be formed at the top surface ofsubstrate 12. In accordance with some embodiments of the presentdisclosure, integrated circuit devices 28 include active devices such astransistors and/or diodes (which may include photo diodes). Integratedcircuit devices 28 may also include passive devices such as capacitors,resistors, or the like. In accordance with alternative embodiments ofthe present disclosure, no active devices are formed, while passivedevices may be formed in photonic die 10.

Over substrate 12 resides dielectric layer 30 (which may also representa plurality of dielectric layers). In accordance with some embodimentsof the present disclosure, dielectric layer 30 is formed of siliconoxide, silicon nitride, or the like. Silicon layer 32 is formed over,and may contact, dielectric layer 30. Silicon layer 32 may be patterned,and is used to form the waveguides for the internal transmission ofoptical signals. Accordingly, silicon layer 32 is also referred to aswaveguide(s) hereinafter. Grating couplers 34 are formed on siliconlayer 32, and the top portions of grating couplers 34 have grating, sothat grating couplers 34 have the function of receiving light ortransmitting light. The grating couplers 34 used for receiving lightreceive the light from the overlying light source or optical signalsource (such as optical fiber 84 as shown FIG. 1G) and transmit thelight to waveguide 32. The grating couplers 34 used for transmittinglight receives light from waveguide 32 and transmit light to fiber 84(FIG. 1G). Modulator(s) 36 are also formed on silicon layer 32, and areused for modulating the optical signals. It is appreciated that photonicdie 10 may include various other devices and circuits that may be usedfor processing and transmitting optical signals and electrical signals,which are also contemplated in accordance with some embodiments of thepresent disclosure.

FIG. 1A also illustrates interconnect structure 38 formed over gratingcouplers 34. Interconnect structure 38 includes a plurality ofdielectric layers 40 and 42 and metal lines and vias (in combinationreferred to as 44) therein. Dielectric layer 40 is formed of alight-transparent material such as silicon oxide. Dielectric layers 42are also referred to as Inter-Metal Dielectrics (IMDs), and may beformed of silicon oxide, silicon oxynitride, silicon nitride, or thelike, or low-k dielectric materials having k values lower than about3.0. The low-k dielectric materials may include Black Diamond (aregistered trademark of Applied Materials), a carbon-containing low-kdielectric material, Hydrogen SilsesQuioxane (HSQ), MethylSilsesQuioxane(MSQ), or the like. Etch stop layers may be formed to separateneighboring IMDs, and are formed of a material(s) having a high etchingselectivity relative to the dielectric layers. The etch stop layers maybe formed of silicon carbide, silicon carbo-nitride, etc. Metal linesand vias 44 may be formed using damascene processes, and may include,for example, copper on diffusion barrier layers. The diffusion barrierlayers may be formed of titanium, titanium nitride, tantalum, tantalumnitride, or the like. In accordance with some embodiments, TVs 14 extendto metal lines 44 in the bottom dielectric layer in dielectric layers42.

Metal pads 48 are formed over and connected to metal lines/vias 44.Passivation layers 46 may be formed, with at least some portions ofpassivation layers 46 covering the edge portions of metal pads 48. Metalpads 48 may be formed of aluminum copper, and hence are referred to asaluminum pads since the majority elements in metal pads 48 are aluminum.Metal pads 48 are electrically connected to the electrical devices (suchas devices 28) and/or through-vias 14 through metal lines and vias 44,which electrical devices may be light-to-electrical conversion devicesand/or electrical-to-light conversion devices. The light-to-electricalconversion devices and/or electrical-to-light conversion devices may bebuilt inside photonic die 10 or external to and attached to photonic die10. The light-to-electrical conversion devices may include photo diodes.The electrical-to-light conversion devices may include light emittingdidoes, lamps, or the like.

Passivation layers 46 may be formed of non-low-k dielectric materials.For example, a passivation layer 46 may include a silicon oxide layerand a silicon nitride layer over the silicon oxide layer. Polymer layerssuch as PBO, polyimide, or the like may or may not be used to form thetop dielectric layers such as layer 49, which is overlying dielectriclayers 46. Electrical connectors 50 are formed at the top surface ofphotonic die 10. In accordance with some embodiments of the presentdisclosure, electrical connectors 50 are formed of copper, nickel,titanium, or multi-layers thereof, and may be formed as metal pillars.Electrical connectors 50 may also include solder caps (not shown).

Holes 52A and 52B are formed in photonic die 10, and penetrate through aplurality of dielectric layers including layers 49, 46, and 42. Holes52A and 52B are also collectively and individually referred to as holes(or openings) 52. The formation of holes 52 includes an etching processusing a photo lithography process. Holes 52 extend to the top surface ofdielectric layer 40, with at least a portion of dielectric layer 40located directly underlying each of holes 52. In accordance with someembodiments of the present disclosure, holes 52 overlap the underlyinggrating couplers 34. The top view shapes of holes 52 may include, andare not limited to, rectangles, circles, hexagons, or the like. It isappreciated that although one hole 52A and one hole 52B are illustrated,there may be a plurality of holes 52A and/or a plurality holes 52B. Inaccordance with some embodiments in which dielectric layers 42 includelow-k dielectric materials, holes 52 may be passivated by covering thesidewalls of holes 52 with a conformal non-low-k dielectric layer (notshown) so that the low-k dielectric materials are not exposed.

Referring to FIG. 1B, electronic die 54 is bonded to photonic die 10.The respective step is illustrated as step 204 in the process flow shownin FIG. 10. The bonding may be achieved through, for example, solderbonding using solder regions 56. Other bonding methods such as directmetal-to-metal bonding or hybrid bonding may also be used. Underfill 58may be dispensed into the gap between electronic die 54 and photonic die10, and is then cured.

In accordance with some embodiments of the present disclosure,electronic die 54 acts as a central processing unit, which includes thecontrolling circuit for controlling the operation of the devices inphotonic die 10. Electronic die 54 also exchanges electrical signalswith photonic die 10 through bonding regions (such as solder regions56). In addition, electronic die 54 includes the circuits for processingthe electrical signals converted from the optical signals in photonicdie 10.

In a subsequent step, as shown in FIG. 1C, adapter 60 is attached tophotonic die 10. The respective step is illustrated as step 206 in theprocess flow shown in FIG. 10. In accordance with some embodiments ofthe present disclosure, adapter 60 is attached to photonic die 10through adhesive 62. In accordance with alternative embodiments of thepresent disclosure, adapter 60 is attached to photonic die 10 throughbonding, for example, fusion bonding (dielectric-to-dielectric) bonding.The bonding may be achieved through, for example, silicon-to-oxidebonding or oxide-to-oxide bonding, in which the oxide may include oxygenatoms. In the bonding, alignment mark(s) 73 in adapter 60 is used foraligning adapter 60 to photonic die 10, so that holes 66A and 66B(collectively or individually referred to as holes or openings 66) inadapter 60 are aligned to the respective underlying holes 52A and 52B,respectively. In accordance with some embodiments of the presentdisclosure, holes 66 have lateral dimensions greater than the lateraldimensions of the corresponding underlying holes 52. Holes 66 may extendlaterally beyond the edges of the corresponding underlying holes 52.Holes 66A and the underlying holes 52A may have a one-to-onecorrespondence, with each of holes 66A overlapping one hole 52A. Holes66A and the underlying holes 52A may have a one-to-many correspondence,with each of holes 66A overlapping a plurality of (two or more) holes52A. Holes 66B and the underlying holes 52B may have a one-to-onecorrespondence, with each of holes 66B overlapping one hole 52B. Holes66B and the underlying holes 52B may also have a one-to-manycorrespondence, with each of holes 66B overlapping a plurality of (twoor more) holes 52B.

FIGS. 6A through 6C illustrate the cross-sectional view of intermediatestages in the formation of adapter 60 in accordance with someembodiments of the present disclosure. Referring to FIG. 6A, blank plate68 is provided. In accordance with some embodiments of the presentdisclosure, blank plate 68 is formed of a homogenous material 72. Also,there is no active devices and passive devices formed on blank plate 68.Blank plate 68 may be formed of a semiconductor material, a dielectricmaterial, or a metallic material. Blank plate 68 may also be formed of amaterial having a Coefficient of Thermal Expansion (CTE) smaller thanthe CTE of the encapsulating material 74 (FIG. 1D). The CTE of blankplate 68 may also be equal to or close to the CTE of silicon (around 2.6ppm/° C.), or between the CTE of silicon and the CTE of theencapsulating material 74. In accordance with some embodiments of thepresent disclosure, blank plate 68 is formed of a semiconductor materialsuch as silicon, and may be in the form of a blank silicon wafer. Inaccordance with alternative embodiments, blank plate 68 is formed of adielectric material such as silicon oxide or silicon nitride (with CTEequal to about 3.2 ppm/° C.). In accordance with yet alternativeembodiments, blank plate 68 is formed of a metallic material such ascopper (with CTE equal to about 8.4 ppm/° C.), aluminum, stainlesssteel, or the like.

Referring to FIG. 6B, holes 52A and 52B are formed to extend from thetop surface of blank plate 68 to an intermediate level in blank plate68. Holes 52A and 52B may be formed through etching. The etching isanisotropic, so that the sidewalls of holes 52A and 52B are straight andvertical.

Next, referring to FIG. 6C, liner 70 is formed on base material 72. Whenplate 68 is a silicon plate or silicon wafer, liner 70 may be formedthrough the thermal oxidation of plate 68, and hence liner 70 is asilicon oxide layer. In accordance with these embodiments, liner 70 mayalso be formed on the sidewalls and the bottom surface of plate 68,which portions of liner 70 are not shown. In accordance with someembodiments of the present disclosure, liner 70 is formed throughdeposition, and liner 70 may include silicon oxide, silicon nitride, orthe like. Liner 70 may be a single layer formed of a homogenous materialsuch as silicon oxide, or may be a composite layer including a pluralityof sub layers formed of different materials. For example, Liner 70 mayinclude a silicon oxide layer, and a titanium nitride layer over thesilicon oxide layer. The formation may be performed using a conformaldeposition method such as Atomic Layer Deposition (ALD), Chemical VaporDeposition (CVD), or the like.

Adhesive film 62 may be formed on the top surface of liner 70 inaccordance with some embodiments for the subsequent attachment. Inaccordance with alternative embodiments, adhesive film 62 is not formed.Furthermore, alignment marks 73 are formed. It is noted that alignmentmarks may be notches extending into plate 68. Next, plate 68 is sawedapart into a plurality of identical adapters 60, and one of the adapters60 is attached to photonic die 10, as shown in FIG. 1C. When adapter 60is attached to photonic die 10 through fusion bonding, no adhesive isdisposed on plate 68. Accordingly, adhesive 62 in FIG. 1C is illustratedas dashed to indicate it may or may not be present.

FIG. 7A illustrates the formation of adapters 60 in accordance withalternative embodiments. The initial structures, materials, and processsteps are also the same as shown in FIGS. 6A and 6B. Next, as shown inFIG. 7A, liner 70 and transparent filling material 71 are formed, andthe top surface of liner 70 and transparent filling material 71 may beplanarized, for example, in a Chemical Mechanical Polish (CMP) ormechanical grinding. Transparent filling material 71 has a firstrefractive index (n₁) greater than a second refractive index (n₂) ofliner 70. Accordingly, transparent filling material 71 may be used totransmit light, and total reflection may occur in transparent fillingmaterial 71 when the light transmitted in transparent filling material71 reaches the liner 70. In accordance with some embodiments of thepresent disclosure, transparent filling material 71 is formed of siliconoxide, silicon nitride, silicon, glass, or the like, and the formationmethods may include deposition or spin-on coating. After theplanarization of liner 70 and transparent filling material 71, plate 68is sawed into adapters 60. Adhesive may or may not be disposed on plate68, depending on the material of liner 70 and the intended method forattaching adapter 60 onto photonic die 10.

FIGS. 7B through 7G illustrate the top views and cross-sectional viewsin the formation of adapters 60 in accordance with alternativeembodiments. Referring to FIG. 7B, which is a cross-sectional view,semiconductor plate 68 is provided. Semiconductor plate 68 may be asilicon substrate, or may be formed of other transparent semiconductormaterials. Openings 69A and 69B are formed in semiconductor plate 68,for example, through etching. FIG. 7C illustrates a top view ofsemiconductor plate 68. Openings 69A and 69B each forms a ringencircling a portion 68′ of semiconductor plate 68.

Next, as shown in FIGS. 7D and 7E, a thermal oxidation is performed toform oxide regions 77, which may be silicon oxide regions. Due to thevolume increase in the thermal oxidation, openings 69A and 69B arefilled by the oxide regions, which forms oxide rings, and are referredto as oxide rings 77A and 77B, respectively. Oxide region 77 alsoincludes a portion on top of semiconductor plate 68.

Next, as shown in FIGS. 7F and 7G, at least some horizontal portions ofoxide regions 77 are removed. In accordance with some embodiments of thepresent disclosure, the horizontal portions of oxide region 77 areremoved in a CMP or mechanical polish step. Semiconductor portions 68′are thus exposed. Alternatively, an etching is performed to removeportions of oxide region 77 covering portions 68′, while leaving otherportions of oxide region 77 not etched. Semiconductor plate 68 is thensawed into adapters 60, which are used in the structure in FIG. 2. Inaccordance with these embodiments, oxide rings 77A and 77B formwaveguides for conducting light, and semiconductor portions 68′ are thetransparent material 71 (in openings 66A and 66B) as shown in FIG. 2.The bonding of the respective adapter 60 to the underlying photonic die10 (FIG. 2) may be fusion bonding.

After the adapter 60 as shown in FIG. 6C or FIG. 7A is attached tophotonic die 10, an encapsulation process is performed to encapsulateadapter 60 and electronic die 54 in encapsulating material 74, as shownin FIG. 1D. The respective step is illustrated as step 208 in theprocess flow shown in FIG. 10. Encapsulating material 74 may be amolding compound, which may include a base material (a polymer or resin)and a filler in the base material. The filler may be sphericalparticles.

FIG. 1E illustrates the planarization of encapsulating material 74,which may be performed through CMP or mechanical grinding. Therespective step is illustrated as step 210 in the process flow shown inFIG. 10. During the planarization, encapsulating material 74, adapter60, and possibly electronic die 54 are thinned. As a result, openings52A, 52B, 66A, and 66B are exposed. Openings 66A and 66B penetratethrough adapter 60, and hence become through-holes. In the resultingstructure, the top surfaces of encapsulating material 74, adapter 60,and electronic die 54 are coplanar with a planar surface. This providesthe advantageous features for subsequent process steps, in which theplanar surface may be placed on another carrier (not shown) in order toperform some process steps (for example, the steps shown in FIGS. 5C and5D). In addition, since electronic die 54 is attached to a part ofphotonic die 10, photonic die may have warpage under stress, causing thecold joint between electronic die 54 and photonic die 10. Photonic die10 may also crack under the stress. The adoption of adapter 60 alsoreduces the stress (particular when the CTE of adapter 60 is close tothat of photonic die 10 and electronic die 54).

The process steps shown in FIGS. 1A through 1E are at wafer level.Accordingly, in the steps shown in FIGS. 1B and 1C, a plurality ofidentical electronic dies 54 and a plurality of identical adapters 60are attached to a plurality of photonic dies 10 in wafer 6. As a result,the structure shown in FIG. 1E is also at wafer level, and the resultingstructure over adhesive 4 is referred to as composite wafer 76.

Composite wafer 76 is then de-mounted from carrier 2, and is attached todicing tape 75, as shown in FIG. 1F. Next, composite wafer 76 issingulated to generate a plurality of packages 78, which are identicalto each other. The respective step is illustrated as step 212 in theprocess flow shown in FIG. 10.

FIG. 1G illustrates the bonding of package 78 to package component 80,which may be a package substrate, a printed circuit board, or the like.Solder regions 26 are reflowed to join bond pads 81 in package component80.

Also, coupler 82 and lamp 86 are attached to package 78. The respectivestep is illustrated as step 214 in the process flow shown in FIG. 10.Coupler 82 is aligned to holes 66A and 52A. Coupler 82 is used for theinput/output of optical signals for photonic die 10. Coupler 82 includesoptical fiber 84, which represents one or a plurality of optical fibers.Optical fiber 84 may penetrate through opening 66A and extend intoopening 52A, and optical fiber 84 is optically coupled to the underlyinggrating coupler 34. Either the light transmitted in optical fiber 84 isprojected onto grating coupler 34, or the light emitted out of gratingcoupler 34 is received by optical fiber 84.

In addition, radiation source 86, which may be a lamp, and hence isalternatively referred to as lamp 86, is attached to photonic die 10,and is aligned to holes 66B and 52B. Lamp 86 is configured to projectlight 88 (which may be a laser beam) into openings 66B and 52B, withlight 88 being projected onto one or a plurality of underlying gratingcouplers 34.

In accordance with some embodiments of the present disclosure, opticaladhesive 90, which is a clear (and hence is transparent) adhesive, isused to fix coupler 82 and lamp 86 onto photonic die 10. Opticaladhesive 90 may be filled into openings 66A, 66B, 52A, and 52B also.Alternatively, optical adhesive 90 may be dispensed over and surroundingcoupler 82 and lamp 86, while leaving openings 66A, 66B, 52A, and 52B asair gaps in the final product. Package 100 is thus formed.

FIGS. 2, 3, 4A-4D, and 5A-5D illustrate the cross-sectional views ofintermediate stages in the formation of packages in accordance with someembodiments of the present disclosure. Unless specified otherwise, thematerials and the formation methods of the components in theseembodiments are essentially the same as the like components, which aredenoted by like reference numerals in the embodiments shown in FIGS. 1Athrough 1G. The details regarding the formation process and thematerials of the packages may thus be found in the discussion of theembodiment shown in FIGS. 1A through 1G.

FIG. 2 illustrates package 100 in accordance with some embodiments ofthe present disclosure. The adapter 60 in accordance with theseembodiments is formed using the process shown in FIG. 7A or the processshown in FIGS. 7B through 7G. Accordingly, the adapter 60 as shown inFIG. 2 includes transparent filling material 71. Transparent fillingmaterial 71 overlaps openings 52A and 52B, which are also air gaps.After the encapsulation and the planarization, filling material 71 inadapter 60 is exposed. Accordingly, in accordance with theseembodiments, through-holes 66A and 66B are filled with transparentfilling material 71. Coupler 82 and lamp 86 are then attached. Inaccordance with these embodiments, optical fiber 84 has a bottom endlevel with or higher than the top surface of adapter 60. The lightprojected from one of optical fibers 84 passes through transparentfilling material 71, and is received by one of grating couplers 34. Thelight projected from one of grating couplers 34 may also pass throughtransparent filling material 71, and is received by a corresponding oneof optical fibers 84. A two-way optical communication is achieved. Inaccordance with these embodiments, optical adhesive 90 is also used tofix coupler 82 and lamp 86. Since there is no opening in adapter 60.Openings 52A and 52B may not be filled with optical adhesive 90, and mayremain as air gaps in the final product.

FIG. 3 illustrates package 100 in accordance with some embodiments ofthe present disclosure. Some of the lamps, which are discretecomponents, are small and thin enough, and hence can fit inside opening66B in the final product without having any portion protruding higherthan the top surface of adapter 60. In accordance with some embodimentsof the present disclosure, lamp 86 is bonded to photonic die 10 throughbond pads. Adapter 60 is then attached, followed by the encapsulationand planarization. During the attachment of adapter 60, lamp 86 isinserted into opening 66B. Lamp 86 receives power from the underlyingphotonic die 10, and no external line is needed to provide power to lamp86. Accordingly, the co-planarity of package 78 is not adverselyaffected by lamp 86. Coupler 82 is then attached, and optical adhesive90 is also dispensed to fix coupler 82. Optical adhesive 90 may bedispensed into openings 66A and 52A, and may or may not be dispensedinto opening 52B. Accordingly, opening 52B may be left as an air gap, orfilled with optical adhesive 90.

The embodiments shown in FIGS. 1A through 1G are performed at waferlevel. Accordingly, during the process shown in FIGS. 1A through 1E,photonic die 10 is part of an un-sawed wafer 6, which includes aplurality of photonic dies 10. The wafer is sawed in the step shown inFIG. 1F. FIGS. 4A through 4D illustrate a die-level formation of package100 in accordance with some embodiments of the present disclosure.

In FIG. 4A, discrete photonic die 10, which has already been sawed fromthe respective wafer, is placed over carrier 2, which is a much smallercarrier than the carrier 2 shown in FIG. 1A. Holes 52A and 52B areformed in photonic dies, and holes 52A and 52B may be formed before thesawing of the wafer in accordance with some embodiments. In accordancewith alternative embodiments, holes 52A and 52B are formed after thesawing of the wafer. Electronic die 54 is bonded to photonic die 10, andunderfill 58 is dispensed and cured.

Next, referring to FIG. 4B, adapter 60 is attached to photonic die 10,for example, through adhesion using an adhesive or throughdielectric-to-dielectric bonding. The adapter 60 in accordance with someembodiments may be formed by performing the steps shown in FIGS. 6Athrough 6C first, and then performing a CMP or grinding to remove excessportions of plate 68, so that openings 52A and 52B becomethrough-openings that penetrate through plate 68. Plate 68 is then sawedapart into a plurality of adapters 60, with one of the adapters 60having the structure shown in FIG. 4B. The height of adapter 60 isselected during the CMP of plate 68, so that the top surface of adapter60 is planar with the top surface of die 54 as much as possible.

Referring to FIG. 4C, adhesive 94 is dispensed between adapter 60 andelectronic die 54, so that adapter 60 and electronic dies 54 arestructurally joined. Adhesive 94 may also be dispensed to encircle (whenviewed in the top view) each of adapter 60 and electronic die 54. Thetop surface of adhesive 94 is slightly lower than the top surfaces ofadapter 60 and electronic dies 54. Package 78 is thus formed.

In FIG. 4D, coupler 82 and lamp 86 are attached to package 78, andoptical adhesive 90 is dispensed. Furthermore, package 78 is bonded topackage component 80. Package 100 is thus formed.

The embodiments shown in FIGS. 1A through 1G are referred to as asolder-first process (or C4-first process since solder regions 26 aresometimes referred to as C4 bumps), in which solder regions 26 areformed before the bonding/attaching of electronic die 54 and adapter 60.FIGS. 5A through 5D illustrate the intermediate steps of a solder-lastprocess, in which solder regions are formed after electronic die 54 andadapter 60 are bonded/attached to photonic die 10. Referring to FIG. 5A,an un-sawed wafer 6, which includes a plurality of photonic dies 10, ismounted on carrier 2 through adhesive 4. In photonic die 10, TVs 14extend to an intermediate level of substrate 12, and do not penetratethrough substrate 12 at this time.

Next, the process steps shown in FIGS. 1B through 1E are performed,resulting in the structure shown in FIG. 5B. The process steps and thematerials may be found in the discussion of the embodiments shown inFIGS. 1B through 1E, and hence are not repeated herein. Composite wafer76 is thus formed.

A carrier swap is then performed, in which carrier 96 (FIG. 5C) is firstattached to the composite wafer 76, for example, through adhesive 98,followed by the demounting of composite wafer 76 from carrier 2 (FIG.5B). The resulting structure is shown in FIG. 5C. Next, a backsidegrinding is performed to remove some backside portions of substrate 12,and hence TVs 14 are exposed. Substrate 12 may then be etched slightlyso that TVs 14 protrude out of the back surface of substrate 12. Insubsequent steps, dielectric layers 18 and 20, RDLs 22, UBMs 24, andsolder regions 26 are formed. The resulting composite wafer 76 is shownin FIG. 5D.

In a subsequent step, composite wafer 76 is demounted from carrier 96.The subsequent steps are essentially the same as shown in FIGS. 1F and1G, and hence are not repeated herein. The resulting package isessentially the same as shown in FIG. 1G.

It is noted that in accordance with various embodiments discussed above,some of the components in the packages 100 have different variations.For example, adapter 60 may or may not include a transparent fillingmaterial in its openings, the package 100 may be formed at wafer-levelor at die-level, and may be formed using solder-first or solder-lastprocess. Lamp 86 may be placed over adapter 60 or inserted into adapter60. These process steps and structures in accordance with the variationsof embodiments may be mixed in any combination whenever applicable. Forexample, in the embodiments shown in FIGS. 4A through 4D and 5A through5D, the transparent filling material (FIG. 2) may be adopted, or lamp 86may be inserted into adapter 60 similar to the embodiments in FIG. 3.

FIG. 8 illustrates the top view of the portion of adapter 60 in package100 in accordance with some exemplary embodiments. In accordance withsome embodiments of the present disclosure, one opening 66A (marked as66A1) overlaps a plurality of openings 52A, and each of openings 52A maybe used for inserting one optical fiber therein. In accordance withother embodiments of the present disclosure, a plurality of openings66A2 are formed, and each opening 66A2 overlap one opening 52A with aone-to-one correspondence, with each of openings 52A/66A2 being used forinserting one optical fiber therein. Opening 66B corresponds to oneopening 52B in accordance with some embodiments.

FIG. 9 illustrates the top view of adapter 60 in accordance withalternative embodiments. This structure is similar to the structureshown in FIG. 8, except opening 66B corresponds to a plurality ofopenings 52B.

In accordance with some embodiments of the present disclosure, someexemplary processes and features are discussed in accordance with someembodiments of the present disclosure. Other features and processes mayalso be included. For example, testing structures may be included to aidin the verification testing of the 3D packaging or 3DIC devices. Thetesting structures may include, for example, test pads formed in aredistribution layer or on a substrate that allows the testing of the 3Dpackaging or 3DIC, the use of probes and/or probe cards, and the like.The verification testing may be performed on intermediate structures aswell as the final structure. Additionally, the structures and methodsdisclosed herein may be used in conjunction with testing methodologiesthat incorporate intermediate verification of known good dies toincrease the yield and decrease costs.

The embodiments of the present disclosure have some advantageousfeatures. The adoption of the adapter may result in a planar topsurface, which may be adhered to carrier in some process steps such asin the formation of solder regions in solder-last process. In addition,the adapter may reduce and balance the stress in the resultingstructure, particularly when the CTE of the adapter is similar to thatof the interposer die and the electronic die. The problem resulting fromthe stress is thus avoided.

In accordance with some embodiments of the present disclosure, a methodincludes bonding an electronic die to a photonic die, wherein thephotonic die comprises a first opening; attaching an adapter onto thephotonic die, wherein a portion of the adapter is at a same level as aportion of the electronic die; forming a through-hole penetratingthrough the adapter, wherein the through-hole is aligned to the firstopening; and attaching an optical device to the adapter, wherein theoptical device is configured to emit a light into the photonic die orreceive a light from the photonic die. In an embodiment, the methodfurther includes after the adapter is attached to the photonic die,encapsulating the electronic die and the adapter in an encapsulatingmaterial; and performing a planarization to remove top portions of theadapter and the electronic die, wherein the through-hole is exposedafter the planarization. In an embodiment, the optical device comprisesa coupler, and in the attaching the optical device, an optical fiber ofthe coupler extends into the through-hole and the first opening. In anembodiment, the photonic die further comprises a second opening, and theadapter further comprises an additional through-hole aligned to thesecond opening, and the method further comprises attaching a lampaligned to the second opening. In an embodiment, the photonic die is adiscrete die that has been sawed from a wafer, and the method furthercomprises: after the adapter is attached to the photonic die, dispensingan adhesive between the adapter and the electronic die. In anembodiment, the attaching the optical device to the adapter comprisesdisposing at least a portion of the optical device overlapping theadapter. In an embodiment, the photonic die further comprises a secondopening, and the method further comprises: bonding a lamp to thephotonic die, wherein after the adapter is attached, the lamp is locatedin the second opening in the adapter. In an embodiment, the methodfurther comprises forming the adapter comprising: forming an opening ina blank plate; forming a protection layer extending into the opening;and sawing the blank plate having the opening to form a plurality ofadapters, with the adapter being one of the plurality of adapters.

In accordance with some embodiments of the present disclosure, a methodincludes forming an adapter, which includes forming a first opening in ablank plate; and forming a protection layer having a portion extendinginto the first opening; attaching the adapter onto a photonic die,wherein the photonic die is in a wafer; bonding an electronic die ontothe photonic die; encapsulating the electronic die and the adapter in anencapsulating material; performing a planarization on the encapsulatingmaterial to expose the adapter, the first opening in the adapter, andthe electronic die; and sawing the encapsulating material and the waferto form a plurality of packages, wherein one of the packages comprisesthe adapter, the photonic die, and the electronic die. In an embodiment,the method further includes forming a second opening in the photonicdie, wherein after the adapter is attached to the photonic die, thefirst opening is joined with the second opening to form a continuousopening. In an embodiment, the method further comprises attaching acoupler to the adapter, wherein an optical fiber of the coupler extendsinto the first opening. In an embodiment, the optical fiber of thecoupler further extends into an additional opening in the photonic die.In an embodiment, the method further includes forming a through-via inthe photonic die, wherein the through-via penetrates through asemiconductor substrate in the photonic die; and forming a solder regionto electrically couple to the through-via. In an embodiment, the formingthe adapter comprises forming a second opening in the adapter, and themethod further comprises: attaching a lamp on top of the adapter,wherein the lamp is directly over the second opening. In an embodiment,the forming the adapter comprises forming a second opening in theadapter, and disposing a lamp inside the second opening of the adapter.

In accordance with some embodiments of the present disclosure, a packageincludes a photonic die comprising a first opening; an electronic dieover and bonded to the photonic die; an adapter over and attached to thephotonic die, wherein the adapter comprises a through-hole penetratingthrough the adapter, and the through-hole is aligned to the firstopening; and an optical coupler, wherein a portion of the opticalcoupler overlaps the through-hole in the adapter. In an embodiment, aportion of the adapter is at a same level as a portion of the electronicdie. In an embodiment, the photonic die further comprises a secondopening, and the package further comprises a lamp overlapping the secondopening. In an embodiment, the optical coupler comprises an opticalfiber extending into the through-hole and the first opening. In anembodiment, the adapter comprises a silicon layer, with no active deviceand passive device formed on the silicon layer.

In accordance with some embodiments of the present disclosure, a methodincludes forming a first opening and a second opening in a photonic die;bonding an electronic die over the photonic die; attaching a siliconadapter onto the photonic die, wherein the silicon adapter is free fromactive devices and passive devices therein, and a third opening of thesilicon adapter is directly over the first opening; and planarizing topsurfaces of the silicon adapter and the electronic die, wherein aportion of the silicon adapter is removed to expose both the firstopening and the second opening, and the third opening becomes athrough-hole penetrating through the silicon adapter. In an embodiment,the method further includes encapsulating the silicon adapter and theelectronic die in an encapsulating material, wherein in the planarizing,the encapsulating material, the silicon adapter and the electronic dieare thinned. In an embodiment, the method further includes forming aprotection layer on the silicon adapter, wherein the protection layerextends into the third opening. In an embodiment, the method furtherincludes attaching an optical coupler to the silicon adapter, whereinthe optical coupler is aligned to the first opening and the thirdopening. In an embodiment, the method further includes attaching a lampto the silicon adapter, wherein the lamp is aligned to the secondopening.

In accordance with some embodiments of the present disclosure, a packageincludes a photonic die comprising a first hole and a second hole; asilicon adapter over and attached to the photonic die, wherein thesilicon adapter comprises a third hole and a fourth hole aligned to, andjoined to, the first hole and the second hole, respectively; an opticalcoupler overlapping the first hole and the third hole; and a lampoverlapping the second hole and the fourth hole. In an embodiment, thesilicon adapter is free from active devices and passive devices therein.In an embodiment, the optical coupler comprises an optical fiberextending into both the first hole and the third hole.

In accordance with some embodiments of the present disclosure, a packageincludes a photonic die comprising a first hole; an adapter over andattached to the photonic die, wherein the adapter comprises a secondhole aligned to, and joined to, the first hole, and the adaptercomprises a first top surface; a molding compound surrounding theadapter, wherein the molding compound comprises a second top surface; anoptical adhesive over and contacting the first top surface and thesecond top surface; and an optical coupler overlapping the first hole,wherein the optical coupler has at least a portion in the opticaladhesive. In an embodiment, the photonic die further comprises a thirdhole, and the adapter further comprises a fourth hole aligned and joinedto the third hole, and the package further comprises a lamp overlappingthe third hole.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A package comprising: a photonic die comprising afirst hole and a second hole; a silicon adapter over and attached to thephotonic die, wherein the silicon adapter comprises a third hole and afourth hole aligned to, and joined to, the first hole and the secondhole, respectively; an optical coupler comprising a portion overlappingthe first hole and the third hole; and a lamp overlapping the secondhole and the fourth hole.
 2. The package of claim 1, wherein the opticalcoupler further comprises an optical fiber, wherein the optical fiberextends into both of the first hole and the third hole.
 3. The packageof claim 1, wherein the silicon adapter comprises a dielectric linerlining sidewalls of the first hole and the second hole.
 4. The packageof claim 1 further comprising an adhesive adhering the silicon adapterto the photonic die.
 5. The package of claim 1 further comprising anencapsulant encapsulating the silicon adapter therein.
 6. The package ofclaim 5 further comprising an electronic die bonded to the photonic die,wherein the encapsulant further encapsulates the electronic die therein.7. The package of claim 6 further comprising an underfill between theelectronic die and the photonic die.
 8. The package of claim 1 furthercomprising an optical adhesive filling the second hole and the fourthhole.
 9. A package comprising: a photonic die comprising a first hole;an adapter over and attached to the photonic die, wherein the adaptercomprises a second hole aligned to, and joined to, the first hole, andthe adapter comprises a first top surface, wherein the adaptercomprises: a silicon-based structure; and an oxide layer lining thesecond hole; a molding compound encircling the adapter, wherein themolding compound comprises a second top surface; an optical adhesiveover and contacting the first top surface and the second top surface;and an optical coupler comprising a potion overlapping the first hole,wherein the optical coupler is at least partially in the opticaladhesive.
 10. The package of claim 9, wherein the optical adhesivefurther extends into the first hole.
 11. The package of claim 9, whereinthe optical adhesive further extends into the second hole.
 12. Thepackage of claim 9, wherein the optical coupler comprises an opticalfiber extending into the first hole and the second hole.
 13. The packageof claim 9, wherein the silicon-based structure comprises a bottomsurface, and the oxide layer comprises a portion contacting the bottomsurface of the silicon-based structure to form a horizontal interface.14. The package of claim 9 further comprising an adhesive between andcontacting the adapter and the photonic die.
 15. The package of claim14, wherein the molding compound is further in physical contact with theadhesive.
 16. The package of claim 9 further comprising an electronicdie bonded to the photonic die, wherein the electronic die isencapsulated in the molding compound.
 17. A package comprising: aphotonic die; an electronic die over and bonded to the photonic die; anadapter over and attached to the photonic die; an optical coupleraligned to a first portion of the adapter, wherein the optical couplercomprises an optical fiber configured to optically couple to a firstoptical device in the photonic die through the adapter; and a radiationsource over and aligned to a second portion of the adapter, wherein theradiation source is configured to optically couple to a second opticaldevice in the photonic die through the adapter.
 18. The package of claim17, wherein top surfaces of the adapter and the electronic die arecoplanar.
 19. The package of claim 17 further comprising an encapsulantencapsulating the adapter and the electronic die therein, wherein topsurfaces of the adapter, the encapsulant, and the electronic die arecoplanar.
 20. The package of claim 19, wherein the adapter comprises: asilicon-based plate; and a silicon oxide liner lining sidewalls of afirst through-hole and a second through-hole of the silicon-based plate,wherein the optical coupler and the radiation source are opticallycoupled to the photonic die through the first through-hole and thesecond through-hole.